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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 25th Jun 2020, 10:56 am   #1
Jon_G4MDC
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Default Pye PF8 Circuit

I wonder if anyone can help with this?

The PF8 was constructed using plug in modules some of which were conventional contruction while others were potted in epoxy. Of course the epoxy ones are pretty much unrepairable.

As far as I can remember the PF8 schematic treated each module as a box with only the functional symbol for what it does, multiplier, PLL, AF Amp etc.
Has anyone seen any more detailed info please?

I want to experiment with the DC/DC converter. It used 2x 1.2V NiCads and a DC/DC to ~10V for the main supply - I have no idea why they chose to do that. The DC/DC Converter is one of the "fixable" modules so the circuit could be traced out if needs be.

I would like to see if it would be safe to run it from a single 3.7V Lithium Cell or if it could be modified to do so.
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Old 26th Jun 2020, 9:19 am   #2
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Default Re: Pye PF8 Circuit

I haven't got a circuit but referencing the late Chris Lorek's first book on pmr conversions he says "connect a suitable 2.4v supply but NEVER (his emphasis) exceed 2.7v otherwise you're likely to damage the set's circuitry" suggesting I think that some mods will need to be done to facilitate 3.7v
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Old 26th Jun 2020, 9:26 am   #3
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Default Re: Pye PF8 Circuit

Interesting info. Thanks.
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Old 26th Jun 2020, 10:01 am   #4
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Default Re: Pye PF8 Circuit

This page any use there is a pdf manual at the bottom.

https://sites.google.com/site/g3xbmqrp3/vuhf/pf8


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Old 26th Jun 2020, 3:51 pm   #5
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Default Re: Pye PF8 Circuit

Brilliant Adrian - thank you. There is more in the manual than I recalled.
The inverter circuit is there so it is exactly what I wanted to know.

My own manual is deep down a pile in the shed - now I don't need to scan it.
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Old 26th Jun 2020, 8:33 pm   #6
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Default Re: Pye PF8 Circuit

Now it gets interesting.

I have robbed a scrap set and here we find the Inductor/Transformer is AL21447 - I will be dissecting that.

The main DC/DC switch transistor is X44H260. Er - wassat then?? Might be K44H260.

The plug in PCB has most of the rest of the works.
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Old 26th Jun 2020, 9:56 pm   #7
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Default Re: Pye PF8 Circuit

Here is the ferrite core..
Looks like a gapped core without an adjuster fitted.
I have yet to look up the spec but it should not be too difficult to find.
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Old 27th Jun 2020, 1:33 pm   #8
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Default Re: Pye PF8 Circuit

The transformer has been disassembled now. It revealed why the set was scrapped. A probable impact with the hard deck has caused the ferrite mass to crack the former - there were no supporting legs on the side clips. The secondary winding had a break in it.

Here is my dissection in the hope it might be of some use to others.

I'm thinking to increase the 6 Turn primary to more like 9 Turns to allow for 3.7V instead of 2.4V supply. The original primary winding was 4 parallel strands of wire or ~24 turns total. I will probably cut back to 3 parallel strands for 27 turns total.

I will rewind this core and try it in a lash up first.
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Old 27th Jun 2020, 1:55 pm   #9
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Default Re: Pye PF8 Circuit

Why not build a buck converter to change the (rather nominal) 3.7V from the LiIon cell to a proper 2.4V. Nicads have a very flat discharge curve unlike LiIon.
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Old 27th Jun 2020, 2:00 pm   #10
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Default Re: Pye PF8 Circuit

It's a thought if this doesn't work I suppose. Not much space though!
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